Discovery in keying circuit for a musical instrument

ABSTRACT

An electrical musical instrument includes a series of tone signal sources under the control of upper manual, lower manual and bass pedal key switches operatively connected to an output system. A further keying circuit includes further keyswitch means under the control of the lower manual which selectively operate a current-mode logic network which in turn drives an audio gating means connected through a single bus to the output system. A rhythm pattern generator has one output that keys said bus and a further output that controls enabling circuit means, namely a two-phase driver portion thereof that alternately energizes two current source portions which are respectively connected to the current-mode logic network whereby bass notes corresponding to the lowest and the highest keys depressed on the lower manual are reproduced by the output system in accordance with the rhythm pattern.

United States Patent 1191 Kniepkamp et a].

1451 Apr. 23, 1974 Inventors: Albert E. Kniepkamp, Chicago;

Douglas R. Moore, Niles, both of Ill.

Assignee: Chicago Musical Instrument Co.,

Lincolnwood, 111.

Filed: July 14, 1972 Appl. No.: 271,696

12/1971 Bunger ..84/1.03 1/1973 Hebeisen 6161.. ..s4/1.03

Primary ExaminerRichard B. Wilkinson Assistant ExaminerStanley J. Witkowski Attorney, Agent, or Firm--l-lill, Sherman, Meroni, Gross & Simpson [5 7] ABSTRACT An electrical musical instrument includes a series of 52 us. (:1 s4/1.03, 84/1.17, 84/126, Signal Sources under the PP manual, 84/1316 2 84/DIG 23 lower manual and bass pedal key switches operatively 51 Int. c1. 01011 1/02, 01011 5/00 Connected to an Output System A further keying [58] Field 61 Search 84/1.01, 1.03, 1.17, 1.24, includes further keyswitch means under the 84/DIG 22 DIG 23 1 13 126, DIG 2 tIOl Of the lower manual which selectively operate a current-mode logic network which in turn drives an [56] References Cited audio gating means connected through a single bus to UNITED STATES PATENTS the output system. A rhythm pattern generator has one output that keys said bus and a further output that 3 S controls enabling circuit means, namely a two-phase 111973 3 22; 7 03 driver portion thereof that alternately energizes two 37]295O H1973 Freeman 84/1'03 current source portions which are respectively con- 3:715:442 2/1973 Freeman: 84/l:01 nected to the current-mode logic network whereby 3,725,560 4/1973 Robinson et 84/101 bass notes corresponding to the lowest and the highest 3,432,607 3/1969 Bergman 84/1.l7 y pr ss d n the ow r manual are reproduced 3,548,066 12/1970 Freeman 84/l.03 by the output system in accordance with the rhythm 3,567,838 3/1971 Tennes et al. 84/l.01 pattern, -3,590,129 6/1971 Freeman 84/l.01 3,624,263 11/1971 Uchiyama 84/1.03 19 Claims, 2 Drawing Figures 704 6/G/V4L M UPPER Mam/42 400/0 UPPER MANUAL 7 20 sou e665 KEfsMzrx/es 7455W/7Cl/f5 1 "1 /2 F/L7Ek5 'XPRE55/0A/ M r P Q PREAMP P'DflL.

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KiYSW/TCML-S c/xcu/r Z4615W/7Z7/5S DISCOVERY IN KEYING CIRCUIT FOR A MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention deals with an electronic organ, and more particularly to a dc-keying circuit employed therein by which bass notes corresponding to the highest and lowest depressed keys on a manual are alternately reproduced in accordance with a rhythm pattern.

2. Prior Art In a known circuit that provides up-down keying of bass notes, one circuit path is used for tone signals which are the lowest ones being played and a second path is used for tone signals which are the highest ones being played. I

SUMMARY OF THE INVENTION In accordance with the present invention, the same circuit is used to conduct a tone signal whether it is the highest or the lowest being played so that all the tone signals of the up-down circuitry are collected and conducted on a common bus. This result is enabled by use of a dc-keying circuit which employs only one keyswitch for this feature per tone signal frequency, such switches being single-pole single-throw switches that have one pole in common. Such keyswitch structure acts through a current-mode logic network to control appropriate tone signal gating means. The currentmode logic network includes a series of transistors whose emitter-collector circuits conduct keying potential, there being a first series ofdiodes respectively connecting each transistor base to each adjacent base, and a second series of diodes respectively connected across the diodes of the first series but with reversed polarity. Enabling circuit means are connected to said currentmode logic network, the enabling circuit means being controlled by a rhythm pattern generator.

Accordingly, it is an object of the present invention to provide a musical instrument employing dc-keying by which bass tones are alternately and rhythmically reproduced which correspond in musical key to the highest and lowest of the playing keys that are then manually depressed.

A further object of the present invention is to provide a musical instrument having an automatic high-low note feature which is controlled by dc-keying circuitry.

Another object of the present invention is to provide a circuit of the type described wherein a single collector bus conducts both the high note and the low note ON THE DRAWINGS FIG. 1 is a block diagram of a musical instrument such as an electronic organ constructed in accordance with the present invention; and

FIG. 2 is a circuit diagram of the keying circuit and the enabling circuit shown in FIG. 1.

AS SHOWN ON THE DRAWINGS The principles of this invention are particularly useful when embodied in an electrical musical instrument suchas an electronic organ shown in block diagram in FIG. 1 in simplified form. The musical instrument includes a set of upper manual keys 11, a set of lower manual keys 12 and a set of bass pedal keys 13. Each of the keys 11, 12 and 13 is mechanically associated with a keyswitch which in this embodiment conducts audio signals, the upper manual keyswitches 14, the lower manual keyswitches 15 and the bass pedal keyswitches 16 being respectively connected in circuit with a set of upper manual tab switches 17, a set of lower manual tab switches 18, and a set of bass pedal tab switches 19, the tab switches 17, 18 and 19 being connected to appropriate filters, and if necessary a preamplifier, collectively identified at 20 for providing selected voicing. The signals from the filters 20 are directed to an output system 21 which includes an expression pedal 22, an amplifier 23 and a speaker 24. A set of tone signal sources 25 is connected to the three sets of keyswitches 14, 15 and 16. Normally, to lower the frequency of the tone signals controlled by the bass pedal keyswitches 16, there is provided a divider circuit 26 in series therewith.

The instrument 10 includes a rhythm pattern generator 27 which has four outputs, one output 28 being connected to control a set of rhythm voice signal sources 29 which is connected to the preamp 20 and to the output system 21. The lower manual keyswitches 15 are connected through a shunt path 30 which bypasses the lower manual tab switches 18, the shunt path 30 including an automatic accompaniment modulator 31 which is controlled by another output 32 of the rhythm pattern generator to simulate manual playing on the lower manual keys 12 in accordance with a rhythm pattern even though the keys 12 are held continually depressed. The tab switches 17, 18 and I9 and the filters and preamp 20 may be considered a part of the output system 21. The rhythm pattern generator 27 has two additional outputs 33, 34, the use of which is explained below. The switching pattern of the generator 27 is in accordance with a preselected rhythm, and signals of different pattern appear at each of the outputs 28, 32, 33 and 34. Further, such pattern may be preselected or changed. V In order to provide the circuitry described above with an automatic high-low bass feature, there is provided a keying circuit 35 which comprises further keyswitch means 36, a dc-keying current-mode logic network 37 and an audio gating means 38. The high-low feature further includes enabling circuit means 39 which comprises a two-phase driver 40 and two enable current sources, the low enable current source 41 and the high enable current source 42 being alternatively but oppositely turned on" and off by the two-phase driver 40.

In this embodiment, the further keyswitch means 36 comprises a set of lower manual automatic bass keyswitches, typically 25 in number, and mechanically connected to be actuated by certain of the keys, such certain keys being the keys 12 in this embodiment. A source of dc-potential 43 is connected to the keyswitches 36. Each of the keyswitches 36 is connected to the audio gating means 38 through a section of the currentmode logic network 37. All the signals that are gated by the audio gating means 38 are collected on a single bus 44 which, if desired, has a further divider circuit 45 connected in series therewith. The output 34 of the rhythm pattern generator is connected through an optional percussive envelope keying circuit 46 to the bus 44 by means of a readout or gate 47. Thus whatever tone signals appear on the single bus 44 are keyed or turned on and off by the rhythm pattern generator 27, the tone signals being given a percussive envelope if desired. The other output 33 of the rhythm pattern generator 27 is connected to control the enabling circuit 39 so that only the tone signal controlled by the lowest depressed key 12 and only the tone signal controlled by the highest depressed key 12 can be gated. Thus the output 33 of the rhythm pattern generator 27 is connected to the input of the two-phase driver 40 and the two outputs of the two-phase driver 40 are operatively connected to the keying circuit 35, namely to the ends of the current-mode logic network 37.

In a broad sense, the enable current sources 41, 42 are means for limiting current flow through the current-mode logic network 37, but in a more restricted sense constitute means for providing constant low current flow through current-mode logic network 37.

The circuit details of the keying circuit 35 and the enabling circuit means 39 are shown in FIG. 2. For ease in identification, the further keyswitch means 36 is enclosed in a broken line rectangle as are the currentmode logic network 37 and the audio gating means 38. Also, the two-phase driver is similarly enclosed and identified at 40 as are the means for providing constant current flows or sources 41 and 42. An optional divider driver 48 is illustrated which may be considered as a part of the divider circuit 45.

The keyswitch means 36 of the keying circuit 35 includes a series, typically 25 in number, of single-pole single-throw switches 49 each having a movable element actuated by one of the keys 12, the stationary element 50 of the switches 49 being common to all the switches 49 and being connected to the source of dcpotential 43.

The dc-keying current-mode logic network 37 of the keying circuit 35 includes a series of transistors 51 of the PNP type, each having a base 52, an emitter 53 and a collector 54. Each of the keyswitches 49 is connected in series with the emitter-collector circuit of one of the transistors 51 and through a load resistor 55 to ground. A connection is made between each collector and load resistor 55 through a further resistor 56 to a gate 57, each gate 57 here comprising a pair of diodes 58, 59 the diode 58 being directed to pass keying potential to the bus 44 to ground through a resistor 60 and the diode 59 being directed to conduct keying potential to one of the tone signal sources 25 and thence to ground. When one of the keyswitches 49 is closed, if the transistor 51 is then conducting, there is an emitter-collector current that renders the gating means 57 conductive whereby tone signals can pass from the tone signal source through such diodes to the bus 44. When the transistor 51 is not conductive, no tone signal is coupled or gated to the bus 44. A capacitor 61 is connected between the bus 44 and ground.

Any tone signals on the bus 44 are coupled through a capacitor 62 to the base of transistor 63 of the NPN type which has its base grounded through a resistor 64,

its emitter grounded, and its collector connected to a source of potential through a resistor 65, the tone signals modifying the collector-emitter current and thus appearing onan output terminal 66 which in turn is connected to the divider 45 and thus in series with a further portion of the bus 44 shown in FIG. 1. A capacitor 67 is connected between the collector of the transistor 63 and ground.

The current-mode logic network 37 further includes a first series of diodes 68 which respectively interconnect the bases of adjacent transistors 51. A second series of diodes 69 are respectively connected across the diodes 68 but with their polarity reversed. The bases of the endmost transistors 51 are respectively connected to the current sources 41 and 42.

The two-phase driver 40 of the enabling circuit means 39 has a transistor 70 of the NPN type whose base is connected through an input resistor 71 to the output terminal 33 of the rhythm pattern generator 27. The base of the transistor 70 is further connected to ground through a resistor 76 as is its emitter. lts collector is connected through a resistor 72 to a source of dcpotential and through a resistor 73 to the base of a transistor 74, of the NPN type, the emitter of which is also grounded and the collector of which is also connected through a resistor 75 to a source of dc-potential.

The input signal at 33 to the two-phase driver 40 is either above ground or is at ground and varies between such two potentials in accordance with the rhythm pattern. When the potential at 33 is at ground, the transistor 70 is not conductive and thus a potential appears on the base of the transistor 74 to render it conductive, thereby placing its collector substantially at ground potential. The collector of the transistor 74 is connected by a line 77 to the current source 41 which at that time is likewise substantially at ground potential. in the meantime, the collector of the transistor 70 has a substantial potential that appears thereon and thus also on a line 78 that is connected to the input of the current source 42. When the potential is positive at the point 33, the transistor 70 is conductive, thereby placing its collector and the line 78 substantially at ground potential, thereby placing the collector of the transistor 74 and the line 77 at a positive potential. In this manner, a high voltage signal at the point 33 causes a high voltage signal to appear on the left or low end of the current-mode logic network 37, and the absence of such signal at the point 33 causes a high voltage signal to appear at the right end of the current-mode logic network 37 or high enable current source 42.

The current sources 41 and 42 are constructed identically and therefore a description of one applies to both. The line 78 is connected through an input resistor 79 to the base of an NPN transistor 80 which has a grounded emitter and a collector that is connected through a resistor 81 to a source of dc-potential. The collector of the transistor 80 is connected through a resistor 82 to the base of a PNP transistor 83, its emitter being connected to the source of potential and its collector being connected through a resistor 84 to the base of an NPN transistor 85. The base and the emitter of the transistor 85 are respectively connected through a pair of resistors 86, 87 to a source of negative potential and the collector thereof is connected to the first transistor 51 and to the ends of the first and second series of diodes 68, 69. The structure described serves to limit current that can flow through the emitter-collector circuit of the various transistors 51 and it does so by providing a constant source or sink of current. The current sources 41, 42 are turned off or on by the potential applied to the lines 77, 78 and since the signal on either of those lines is always out of phase with each other, only one of the current sources 41, 42 will be energized at a time, and then in accordance with the command at the point 33. As no claim is made to the internal circuitry of the current sources 41, 42 it is believed that no further description thereof is necessary. It is sufficient to understand that the output current form the current-mode logic network 37 is restricted and is held to a constant value on the order of 5 milliamperes.

When the current source 41 is on, a ground potential appears at the left end of the series of diodes 68, but there is no circuit path therethrough so that at such moment, none of them is conductive. The same potential also appears at the base of the endmost transistor 51. When the corresponding keyswitch 49 is closed, the transistor 51 is rendered conductive and keying potential appears at its collector, there being a diode-type of current flow through the emitter and the base to the current source 41. The potential at the base during conduction will be approximately 0.6 volts less than the keying potential, for example 12.4 volts in this example. Assuming instead that the second keyswitch 49 from the left end is actuated, there will again be a potential on the base which is reduced by 0.6 volts due to the diode effect of the transistor, but there will be a further reduction of 0.6 volts due to the presence of the diode 68. Thus during such operation the potential on the first base can be no higher than 1 1.8 in this example. Each of the succeeding transistors to the right progressively thus causes a maximum base potential on the first base which decreases by 0.6 volts for each diode 68 that separates such transistor from the current source 41. This difference in potential is sufficient so that if two of the keyswitches 49 are actuated simultaneously, the current path for all practical purposes will be only through the transistor closest to the current source 41 and thus no matter how many of the keys 12 are actuated, only a signal corresponding to the lowest key 12 will be gated or coupled. With two keyswitches 49 closed, if both transistors 51 could conduct, the same base potentials of the associated transistors 51 would appear in the series of diodes 68, thus leaving no voltage drop across the intermediate diodes 68. Thus no intermediate diode 68 could be conductive, and thus the right one of the two transistors 51 cannot be rendered conductive. When the other current source 42 is energized, it coacts with the other diodes 69 to work in the same manner so that only the transistor closest to the current source 42 can conduct if more than one key 12 is depressed, thereby providing the from both current sources 41, 42.

Representative values for resistors and capacitors are as follows:

RESISTORS CAPACITORS 4.7K 56 IOOK 60- 22K 64- 100K 65 lOOK 71- 33K 72 10K 73- 22K 75 10K 76- [OK 61 30o pf 62- .0012 mfd 67 1000 pf 7922K 8llOK 82-22K 84-4.7K 86-1K 87-1K The high-low bass circuit operates as follows. The rhythm pattern generator 27 sends pulses through its output 33 to indicate whether the lowest note played on the lower manual should be the basis for bass accompaniment or whether the highest note played on the lower manual should be the basis for bass accompaniment. These signals are interpreted by the two-phase driver 40 which respectively turns the low enable current source or sink on or else turns the high enable current source or sink on. This applies a base potential, such as ground, to the base of the nearest transistor 51 and also to the end of the diode series that is directed to conduct. When any one or more keyswitches 49 are then closed, only the transistor 51 closest to the energized current source or sink will conduct and thus only the corresponding tone signal source 25 is coupled to the bus 44. The signals on the bus 44 are then further keyed so that they reach the output system 21 only in accordance with signals on the output 34 of the rhythm pattern generator 27.

Although various minor modifications might be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon, all such embodiments as reasonably and properly come within the scope of our contribution to the art.

We claim:

1. An electrical musical instrument, comprising:

a. a series of tone signal sources;

b. an output system;

c. keyswitch means connected for supplying tone signals from selected ones of said tone signal sources to said output system;

d. a bus;

e. a keying circuit, actuated with certain ones of the selected keyswitch means and connected for providing keying potentials for coupling the tone signal sources corresponding to the highest and lowest of the selected ones of the certain keyswitches through said bus to said output system;

f. a rhythm pattern generator, adapted to provide control potentials in accordance with a selected rhythm pattern, and having a first output connected to said bus for controlling the tone signals conducted therein; and

enabling circuit means driven by a second output of said rhythm pattern generator andconnected to said keying circuit for alternately enabling the keying potential for said tone signal sources corresponding to only said highest and only said lowest of the selected ones of the certain keyswitches.

2. An electrical musical instrument according to claim 1 including upper manual keys, lower manual keys and bass pedal keys disposed and arranged to actuate said keyswitch means, said certain keyswitch means being actuated by said lower manual keys.

3. An electrical musical instrument according to claim 2 including a divider connected in series with said keyswitch means actuated by said bass pedal keys.

4. An electrical musical instrument according to claim 1 including a percussive envelope keying circuit by which said first output of said rhythm pattern generator is connected to said bus.

5. An electrical musical instrument according to claim 1 including a divider connected in series with said bus.

6. An electrical musical instrument according to claim 1 including a modulator circuit connected in series between said certain of said keyswitch means and said output system and connected to be under the control of a further output of said rhythm pattern generator.

7. An electrical musical instrument according to claim 1 in which said enabling circuit means includes a two-phase driver having an input connected to the second output of the rhythm pattern generator and two driver outputs respectively operatively connected to said keying circuit for enabling said highest and said lowest tone signal sources.

8. An electrical musical instrument according to claim 1 in which said keying circuit includes:

a. further keyswitch means, actuated with said certain keyswitch means, and connected to a source of dc-keying potential;

b. a dc-keying current-mode logic network connected to be energized by said further keyswitch means; and

0. audio gating means interconnecting said tone signal sources with said bus under the control of said logic network.

9. An electrical musical instrument according to claim 8 in which said dc-keying current-mode logic network comprises:

a. A series of transistors each having a base, an emitter and a collector, the emitter-collector circuits of said transistors and said further keyswitch means being respectively connected in series and to said audio gating means;

b. a first series of diodes respectively connecting the base of each said transistor to the base of each adjacent transistor, and a second series of diodes respectively connected with reversed polarity across the diodes of said first series, the endmost transistor bases being connected to said enabling circuit.

10. An electrical musical instrument according to claim 9 in which said enabling circuit means includes a two-phase driver having an input connected to the second output of the rhythm pattern generator and two driver outputs respectively operatively connected to said endmost transistor bases.

11. .An electrical musical instrument according to claim 8 in which said enabling means includes means for limiting current flow in said current mode logic network.

12. An electrical musical instrumentaccording to claim 11 in which said limiting means is a means for providing a constant current flow in said network.

13. An electrical musical instrument according to claim 9 in which said enabling means includes means for limiting current flow through said emitter-collector circuits.

14. An electrical musical instrument according to claim 13 in which said limiting means is a means for providing a constant current flow through said emittercollector circuits. 7

15. An electrical musical instrument according to claim 9 including 'a series of load resistors respectively connected to said collectors.

16. An electrical musical instrument according to claim 7 in which the operative connection includes a pair of means for limiting current flow in said currentmode logic network, and respectively driven alternately on and off by said two-phase driver.

17. An electrical musical instrument according to claim 10 in which the operative connections include a pair of means for limiting current flow through said emitter-collector circuits, and respectively driven alternately on and off by said two-phase driver.

18. An electrical musical instrument according to claim 8 in which said further keyswitch means for the keying potential comprises only one single-pole singlethrow switch per tone signal source couplable to said bus.

19. An electrical musical instrument according to claim 18 in which one of the poles of said single-throw switches is electrically common. 

1. An electrical musical instrument, comprising: a. a series of tone signal sources; b. an output system; c. keyswitch means connected for supplying tone signals from selected ones of said tone signal sources to said output system; d. a bus; e. a keying circuit, actuated with certain ones of the selected keyswitch means and connected for providing keying potentials for coupling the tone signal sources corresponding to the highest and lowest of the selected ones of the certain keyswitches through said bus to said output system; f. a rhythm pattern generator, adapted to provide control potentials in accordance with a selected rhythm pattern, and having a first output connected to said bus for controlling the tone signals conducted therein; and enabling circuit means driven by a second output of said rhythm pattern generator and connected to said keying circuit for alternately enabling the keying potential for said tone signal sources corresponding to only said highest and only said lowest of the selected ones of the certain keyswitches.
 2. An electrical musical instrument according to claim 1 including upper manual keys, lower manual keys and bass pedal keys disposed and arranged to actuate said keyswitch means, said certain keyswitch means being actuated by said lower manual keys.
 3. An electrical musical instrument according to claim 2 including a divider connected in series with said keyswitch means actuated by said bass pedal keys.
 4. An electrical musical instrument according to claim 1 including a percussive envelope keying circuit by which said first output of said rhythm pattern generator is connected to said bus.
 5. An electrical musical instrument according to claim 1 including a divider connected in series with said bus.
 6. An electrical musical instrument according to claim 1 including a modulator circuit connected in series between said certain of said keyswitch means and said output system and connected to be under the control of a further output of said rhythm pattern generator.
 7. An electrical musical instrument according to claim 1 in which said enabling circuit means includes a two-phase driver having an input connected to the second output of the rhythm pattern generator and two driver outputs respectively operatively connected to said keying circuit for enabling said highest and said lowest tone signal sources.
 8. An electrical musical instrument according to claim 1 in which said keying circuit includes: a. further keyswitch means, actuated with said certain keyswitch means, and connected to a source of dc-keying potential; b. a dc-keying current-mode logic network connected to be energized by said further keyswitch means; and c. audio gating means interconnecting said tone signal sources with said bus under the control of said logic network.
 9. An electrical musical instrument according to claim 8 in which said dc-keying current-mode logic network comprises: a. A series of transistors each having a base, an emitter and a collector, the emitter-collector circuits of said transistors and said further keyswitch means being respectively connected in series and to said audio gating means; b. a first series of diodes respectively connecting the base of each said transistor to the base of each adjacent transistor, and a second series of diodes respectively connected with reversed polarity across the diodes of said first series, the endmost transistor bases being connected to said enabling circuit.
 10. An electrical musical instrument according to claim 9 in which said enabling circuit means incluDes a two-phase driver having an input connected to the second output of the rhythm pattern generator and two driver outputs respectively operatively connected to said endmost transistor bases.
 11. An electrical musical instrument according to claim 8 in which said enabling means includes means for limiting current flow in said current mode logic network.
 12. An electrical musical instrument according to claim 11 in which said limiting means is a means for providing a constant current flow in said network.
 13. An electrical musical instrument according to claim 9 in which said enabling means includes means for limiting current flow through said emitter-collector circuits.
 14. An electrical musical instrument according to claim 13 in which said limiting means is a means for providing a constant current flow through said emitter-collector circuits.
 15. An electrical musical instrument according to claim 9 including a series of load resistors respectively connected to said collectors.
 16. An electrical musical instrument according to claim 7 in which the operative connection includes a pair of means for limiting current flow in said current-mode logic network, and respectively driven alternately on and off by said two-phase driver.
 17. An electrical musical instrument according to claim 10 in which the operative connections include a pair of means for limiting current flow through said emitter-collector circuits, and respectively driven alternately on and off by said two-phase driver.
 18. An electrical musical instrument according to claim 8 in which said further keyswitch means for the keying potential comprises only one single-pole single-throw switch per tone signal source couplable to said bus.
 19. An electrical musical instrument according to claim 18 in which one of the poles of said single-throw switches is electrically common. 